Design Pattern Template Method C

痛定思痛。 2022-04-18 00:29 155阅读 0赞

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### **Definition** ###

Define the skeleton of an algorithm in an operation, deferring some steps to subclasses. Template Method lets subclasses redefine certain steps of an algorithm without changing the algorithm's structure.

### Participants ###

The classes and/or objects participating in this pattern are:

*  **AbstractClass** **(DataObject)**
    
     *  Defines abstract *primitive operations* that concrete subclasses define to implement steps of an algorithm
     *  
     *  Implements a template method defining the skeleton of an algorithm. The template method calls primitive operations as well as operations defined in AbstractClass or those of other objects
     *  
 *  
 *  **ConcreteClass** **(CustomerDataObject)**
    
     *  Implements the primitive operations or carry out subclass-specific steps of the algorithm
     *

### Sample Code in C\# ###

This structural code demonstrates the Template method which provides a skeleton calling sequence of methods. One or more steps can be deferred to subclasses which implement these steps without changing the overall calling sequence.

// Template Method pattern - Structural example                    namespace CSharpLearning{    using System;    /// <summary>    /// Startup class for Real-World Template Method design pattern.    /// </summary>    public class MainApp    {        /// <summary>        /// Entry point into console application.        /// </summary>        public static void Main()        {            AbstractClass aA = new ConcreteClassA();            aA.TemplateMethod();            AbstractClass aB = new ConcreteClassB();            aB.TemplateMethod();            // Wait for user.            Console.ReadKey();        }    }    /// <summary>    /// The 'AbstractClass' abstract class.    /// </summary>    public abstract class AbstractClass    {        /// <summary>        /// The primitive operation 1.        /// </summary>        public abstract void PrimitiveOperation1();        /// <summary>        /// The primitive operation 2.        /// </summary>        public abstract void PrimitiveOperation2();        /// <summary>        /// The template method.        /// </summary>        public void TemplateMethod()        {            this.PrimitiveOperation1();            this.PrimitiveOperation2();            Console.WriteLine(string.Empty);        }    }    /// <summary>    /// A 'ConcreteClass' class.    /// </summary>    public class ConcreteClassA : AbstractClass    {        /// <summary>        /// The primitive operation 1.        /// </summary>        public override void PrimitiveOperation1()        {            Console.WriteLine("ConcreteClassA.PrimitiveOperation1()");        }        /// <summary>        /// The primitive operation 2.        /// </summary>        public override void PrimitiveOperation2()        {            Console.WriteLine("ConcreteClassA.PrimitiveOperation2()");        }    }    /// <summary>    /// A 'ConcreteClass' class.    /// </summary>    public class ConcreteClassB : AbstractClass    {        /// <summary>        /// The primitive operation 1.        /// </summary>        public override void PrimitiveOperation1()        {            Console.WriteLine("ConcreteClassB.PrimitiveOperation1()");        }        /// <summary>        /// The primitive operation 2.        /// </summary>        public override void PrimitiveOperation2()        {            Console.WriteLine("ConcreteClassB.PrimitiveOperation2()");        }    }}// Output:/*ConcreteClassA.PrimitiveOperation1()ConcreteClassA.PrimitiveOperation2() ConcreteClassB.PrimitiveOperation1()ConcreteClassB.PrimitiveOperation2()*/

--------------------

This real-world code demonstrates a Template method named Run() which provides a skeleton calling sequence of methods. Implementation of these steps are deferred to the CustomerDataObject subclass which implements the Connect, Select, Process, and Disconnect methods.

// Template Method pattern - Real World examplenamespace CSharpLearning{    using System;    using System.Data;    using System.Data.OleDb;    /// <summary>    /// Startup class for Real-World Template Design Pattern.    /// </summary>    public class MainApp    {        /// <summary>        /// Entry point into console application.        /// </summary>        public static void Main()        {            DataAccessObject daoCategories = new Categories();            daoCategories.Run();            DataAccessObject daoProducts = new Products();            daoProducts.Run();            // Wait for user.            Console.ReadKey();        }    }    /// <summary>    /// The 'AbstractClass' abstract class.    /// </summary>    public abstract class DataAccessObject    {        /// <summary>        /// The connection string.        /// </summary>        protected string ConnectionString;        /// <summary>        /// The data set.        /// </summary>        protected DataSet DataSet;        /// <summary>        /// The connect.        /// </summary>        public virtual void Connect()        {            // Make sure mdb is available to app.            this.ConnectionString = "provider=Microsoft.JET.OLEDB.4.0; data source=..\\..\\..\\db1.mdb";        }        /// <summary>        /// The select.        /// </summary>        public abstract void Select();        /// <summary>        /// The process.        /// </summary>        public abstract void Process();        /// <summary>        /// The disconnect.        /// </summary>        public virtual void Disconnect()        {            this.ConnectionString = string.Empty;        }        /// <summary>        /// The 'Template Method'.        /// </summary>        public void Run()        {            this.Connect();            this.Select();            this.Process();            this.Disconnect();        }    }    /// <summary>    /// A 'ConcreteClass' class.    /// </summary>    public class Categories : DataAccessObject    {        /// <summary>        /// The select.        /// </summary>        public override void Select()        {            const string Sql = "select CategoryName from Categories";            OleDbDataAdapter dataAdapter = new OleDbDataAdapter(Sql, this.ConnectionString);            this.DataSet = new DataSet();            dataAdapter.Fill(this.DataSet, "Categories");        }        /// <summary>        /// The process.        /// </summary>        public override void Process()        {            Console.WriteLine("Categories ---- ");            DataTable dataTable = this.DataSet.Tables["Categories"];            foreach (DataRow row in dataTable.Rows)            {                Console.WriteLine(row["CategoryName"]);            }            Console.WriteLine();        }    }    /// <summary>    /// A 'ConcreteClass' class.    /// </summary>    public class Products : DataAccessObject    {        /// <summary>        /// The select.        /// </summary>        public override void Select()        {            const string Sql = "select ProductName from Products";            OleDbDataAdapter dataAdapter = new OleDbDataAdapter(Sql, this.ConnectionString);            this.DataSet = new DataSet();            dataAdapter.Fill(this.DataSet, "Products");        }        /// <summary>        /// The process.        /// </summary>        public override void Process()        {            Console.WriteLine("Products ---- ");            DataTable dataTable = this.DataSet.Tables["Products"];            foreach (DataRow row in dataTable.Rows)            {                Console.WriteLine(row["ProductName"]);            }            Console.WriteLine();        }    }}// Output:/*Categories ----BeveragesCondimentsConfectionsDairy ProductsGrains/CerealsMeat/PoultryProduceSeafoodProducts ----ChaiChangAniseed SyrupChef Anton's Cajun SeasoningChef Anton's Gumbo MixGrandma's Boysenberry SpreadUncle Bob's Organic Dried PearsNorthwoods Cranberry SauceMishi Kobe Niku*/

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